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rework alias-relate to norm(lhs) == norm(rhs)

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This commit is contained in:
lcnr 2023-11-09 11:06:48 +01:00
parent 1c54494888
commit e3850f404d
4 changed files with 164 additions and 167 deletions
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22
compiler/rustc_middle/src/ty/sty.rs
View File

@ -1245,6 +1245,28 @@ pub fn kind(self, tcx: TyCtxt<'tcx>) -> ty::AliasKind {
}
}
/// Whether this alias type is an opaque.
pub fn is_opaque(self, tcx: TyCtxt<'tcx>) -> bool {
matches!(self.opt_kind(tcx), Some(ty::AliasKind::Opaque))
}
/// FIXME: rename `AliasTy` to `AliasTerm` and always handle
/// constants. This function can then be removed.
pub fn opt_kind(self, tcx: TyCtxt<'tcx>) -> Option<ty::AliasKind> {
match tcx.def_kind(self.def_id) {
DefKind::AssocTy
if let DefKind::Impl { of_trait: false } =
tcx.def_kind(tcx.parent(self.def_id)) =>
{
Some(ty::Inherent)
}
DefKind::AssocTy => Some(ty::Projection),
DefKind::OpaqueTy => Some(ty::Opaque),
DefKind::TyAlias => Some(ty::Weak),
_ => None,
}
}
pub fn to_ty(self, tcx: TyCtxt<'tcx>) -> Ty<'tcx> {
Ty::new_alias(tcx, self.kind(tcx), self)
}

299
compiler/rustc_trait_selection/src/solve/alias_relate.rs
View File

@ -11,18 +11,12 @@
//! * bidirectional-normalizes-to: If `A` and `B` are both projections, and both
//! may apply, then we can compute the "intersection" of both normalizes-to by
//! performing them together. This is used specifically to resolve ambiguities.
use super::{EvalCtxt, SolverMode};
use super::EvalCtxt;
use rustc_infer::infer::DefineOpaqueTypes;
use rustc_infer::traits::query::NoSolution;
use rustc_middle::traits::solve::{Certainty, Goal, QueryResult};
use rustc_middle::ty;
/// We may need to invert the alias relation direction if dealing an alias on the RHS.
#[derive(Debug)]
enum Invert {
No,
Yes,
}
impl<'tcx> EvalCtxt<'_, 'tcx> {
#[instrument(level = "debug", skip(self), ret)]
pub(super) fn compute_alias_relate_goal(
@ -31,187 +25,130 @@ pub(super) fn compute_alias_relate_goal(
) -> QueryResult<'tcx> {
let tcx = self.tcx();
let Goal { param_env, predicate: (lhs, rhs, direction) } = goal;
if lhs.is_infer() || rhs.is_infer() {
bug!(
"`AliasRelate` goal with an infer var on lhs or rhs which should have been instantiated"
let Some(lhs) = self.try_normalize_term(param_env, lhs)? else {
return self.evaluate_added_goals_and_make_canonical_response(Certainty::OVERFLOW);
};
let Some(rhs) = self.try_normalize_term(param_env, rhs)? else {
return self.evaluate_added_goals_and_make_canonical_response(Certainty::OVERFLOW);
};
let variance = match direction {
ty::AliasRelationDirection::Equate => ty::Variance::Invariant,
ty::AliasRelationDirection::Subtype => ty::Variance::Covariant,
};
match (lhs.to_alias_ty(tcx), rhs.to_alias_ty(tcx)) {
(None, None) => {
self.relate(param_env, lhs, variance, rhs)?;
self.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
}
(Some(alias), None) => {
if rhs.is_infer() {
self.relate(param_env, lhs, variance, rhs)?;
self.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
} else if alias.is_opaque(tcx) {
self.define_opaque(param_env, alias, rhs)
} else {
Err(NoSolution)
}
}
(None, Some(alias)) => {
if lhs.is_infer() {
self.relate(param_env, lhs, variance, rhs)?;
self.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
} else if alias.is_opaque(tcx) {
self.define_opaque(param_env, alias, lhs)
} else {
Err(NoSolution)
}
}
(Some(alias_lhs), Some(alias_rhs)) => {
self.relate_rigid_alias_or_opaque(param_env, alias_lhs, variance, alias_rhs)
}
}
}
/// Normalize the `term` to equate it later. This does not define opaque types.
#[instrument(level = "debug", skip(self, param_env), ret)]
fn try_normalize_term(
&mut self,
param_env: ty::ParamEnv<'tcx>,
term: ty::Term<'tcx>,
) -> Result<Option<ty::Term<'tcx>>, NoSolution> {
match term.unpack() {
ty::TermKind::Ty(ty) => {
// We do no define opaque types here but instead do so in `relate_rigid_alias_or_opaque`.
Ok(self
.try_normalize_ty_recur(param_env, DefineOpaqueTypes::No, 0, ty)
.map(Into::into))
}
ty::TermKind::Const(_) => {
if let Some(alias) = term.to_alias_ty(self.tcx()) {
let term = self.next_term_infer_of_kind(term);
self.add_goal(Goal::new(
self.tcx(),
param_env,
ty::ProjectionPredicate { projection_ty: alias, term },
));
self.try_evaluate_added_goals()?;
Ok(Some(self.resolve_vars_if_possible(term)))
} else {
Ok(Some(term))
}
}
}
}
fn define_opaque(
&mut self,
param_env: ty::ParamEnv<'tcx>,
opaque: ty::AliasTy<'tcx>,
term: ty::Term<'tcx>,
) -> QueryResult<'tcx> {
self.add_goal(Goal::new(
self.tcx(),
param_env,
ty::ProjectionPredicate { projection_ty: opaque, term },
));
self.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
}
fn relate_rigid_alias_or_opaque(
&mut self,
param_env: ty::ParamEnv<'tcx>,
lhs: ty::AliasTy<'tcx>,
variance: ty::Variance,
rhs: ty::AliasTy<'tcx>,
) -> QueryResult<'tcx> {
let tcx = self.tcx();
let mut candidates = vec![];
if lhs.is_opaque(tcx) {
candidates.extend(
self.probe_misc_candidate("define-lhs-opaque")
.enter(|ecx| ecx.define_opaque(param_env, lhs, rhs.to_ty(tcx).into())),
);
}
match (lhs.to_alias_ty(tcx), rhs.to_alias_ty(tcx)) {
(None, None) => bug!("`AliasRelate` goal without an alias on either lhs or rhs"),
// RHS is not a projection, only way this is true is if LHS normalizes-to RHS
(Some(alias_lhs), None) => self.assemble_normalizes_to_candidate(
param_env,
alias_lhs,
rhs,
direction,
Invert::No,
),
// LHS is not a projection, only way this is true is if RHS normalizes-to LHS
(None, Some(alias_rhs)) => self.assemble_normalizes_to_candidate(
param_env,
alias_rhs,
lhs,
direction,
Invert::Yes,
),
(Some(alias_lhs), Some(alias_rhs)) => {
debug!("both sides are aliases");
let mut candidates = Vec::new();
// LHS normalizes-to RHS
candidates.extend(self.assemble_normalizes_to_candidate(
param_env,
alias_lhs,
rhs,
direction,
Invert::No,
));
// RHS normalizes-to RHS
candidates.extend(self.assemble_normalizes_to_candidate(
param_env,
alias_rhs,
lhs,
direction,
Invert::Yes,
));
// Relate via args
if rhs.is_opaque(tcx) {
candidates.extend(
self.assemble_subst_relate_candidate(
param_env, alias_lhs, alias_rhs, direction,
),
self.probe_misc_candidate("define-rhs-opaque")
.enter(|ecx| ecx.define_opaque(param_env, rhs, lhs.to_ty(tcx).into())),
);
debug!(?candidates);
}
if let Some(merged) = self.try_merge_responses(&candidates) {
Ok(merged)
} else {
// When relating two aliases and we have ambiguity, if both
// aliases can be normalized to something, we prefer
// "bidirectionally normalizing" both of them within the same
// candidate.
//
// See <https://github.com/rust-lang/trait-system-refactor-initiative/issues/25>.
//
// As this is incomplete, we must not do so during coherence.
match self.solver_mode() {
SolverMode::Normal => {
if let Ok(bidirectional_normalizes_to_response) = self
.assemble_bidirectional_normalizes_to_candidate(
param_env, lhs, rhs, direction,
)
{
Ok(bidirectional_normalizes_to_response)
candidates.extend(self.probe_misc_candidate("args-relate").enter(|ecx| {
ecx.relate(param_env, lhs, variance, rhs)?;
ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
}));
if let Some(result) = self.try_merge_responses(&candidates) {
Ok(result)
} else {
self.flounder(&candidates)
}
}
SolverMode::Coherence => self.flounder(&candidates),
}
}
}
}
}
#[instrument(level = "debug", skip(self), ret)]
fn assemble_normalizes_to_candidate(
&mut self,
param_env: ty::ParamEnv<'tcx>,
alias: ty::AliasTy<'tcx>,
other: ty::Term<'tcx>,
direction: ty::AliasRelationDirection,
invert: Invert,
) -> QueryResult<'tcx> {
self.probe_misc_candidate("normalizes-to").enter(|ecx| {
ecx.normalizes_to_inner(param_env, alias, other, direction, invert)?;
ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
})
}
// Computes the normalizes-to branch, with side-effects. This must be performed
// in a probe in order to not taint the evaluation context.
fn normalizes_to_inner(
&mut self,
param_env: ty::ParamEnv<'tcx>,
alias: ty::AliasTy<'tcx>,
other: ty::Term<'tcx>,
direction: ty::AliasRelationDirection,
invert: Invert,
) -> Result<(), NoSolution> {
let other = match direction {
// This is purely an optimization. No need to instantiate a new
// infer var and equate the RHS to it.
ty::AliasRelationDirection::Equate => other,
// Instantiate an infer var and subtype our RHS to it, so that we
// properly represent a subtype relation between the LHS and RHS
// of the goal.
ty::AliasRelationDirection::Subtype => {
let fresh = self.next_term_infer_of_kind(other);
let (sub, sup) = match invert {
Invert::No => (fresh, other),
Invert::Yes => (other, fresh),
};
self.sub(param_env, sub, sup)?;
fresh
}
};
self.add_goal(Goal::new(
self.tcx(),
param_env,
ty::ProjectionPredicate { projection_ty: alias, term: other },
));
Ok(())
}
fn assemble_subst_relate_candidate(
&mut self,
param_env: ty::ParamEnv<'tcx>,
alias_lhs: ty::AliasTy<'tcx>,
alias_rhs: ty::AliasTy<'tcx>,
direction: ty::AliasRelationDirection,
) -> QueryResult<'tcx> {
self.probe_misc_candidate("args relate").enter(|ecx| {
match direction {
ty::AliasRelationDirection::Equate => {
ecx.eq(param_env, alias_lhs, alias_rhs)?;
}
ty::AliasRelationDirection::Subtype => {
ecx.sub(param_env, alias_lhs, alias_rhs)?;
}
}
ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
})
}
fn assemble_bidirectional_normalizes_to_candidate(
&mut self,
param_env: ty::ParamEnv<'tcx>,
lhs: ty::Term<'tcx>,
rhs: ty::Term<'tcx>,
direction: ty::AliasRelationDirection,
) -> QueryResult<'tcx> {
self.probe_misc_candidate("bidir normalizes-to").enter(|ecx| {
ecx.normalizes_to_inner(
param_env,
lhs.to_alias_ty(ecx.tcx()).unwrap(),
rhs,
direction,
Invert::No,
)?;
ecx.normalizes_to_inner(
param_env,
rhs.to_alias_ty(ecx.tcx()).unwrap(),
lhs,
direction,
Invert::Yes,
)?;
ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
})
}
}

20
compiler/rustc_trait_selection/src/solve/eval_ctxt/mod.rs
View File

@ -751,6 +751,26 @@ pub(super) fn sub<T: ToTrace<'tcx>>(
})
}
#[instrument(level = "debug", skip(self, param_env), ret)]
pub(super) fn relate<T: ToTrace<'tcx>>(
&mut self,
param_env: ty::ParamEnv<'tcx>,
lhs: T,
variance: ty::Variance,
rhs: T,
) -> Result<(), NoSolution> {
self.infcx
.at(&ObligationCause::dummy(), param_env)
.relate(DefineOpaqueTypes::No, lhs, variance, rhs)
.map(|InferOk { value: (), obligations }| {
self.add_goals(obligations.into_iter().map(|o| o.into()));
})
.map_err(|e| {
debug!(?e, "failed to relate");
NoSolution
})
}
/// Equates two values returning the nested goals without adding them
/// to the nested goals of the `EvalCtxt`.
///

26
compiler/rustc_trait_selection/src/solve/mod.rs
View File

@ -16,13 +16,14 @@
//! about it on zulip.
use rustc_hir::def_id::DefId;
use rustc_infer::infer::canonical::{Canonical, CanonicalVarValues};
use rustc_infer::infer::DefineOpaqueTypes;
use rustc_infer::traits::query::NoSolution;
use rustc_middle::infer::canonical::CanonicalVarInfos;
use rustc_middle::traits::solve::{
CanonicalResponse, Certainty, ExternalConstraintsData, Goal, IsNormalizesToHack, QueryResult,
Response,
};
use rustc_middle::ty::{self, Ty, TyCtxt, UniverseIndex};
use rustc_middle::ty::{self, OpaqueTypeKey, Ty, TyCtxt, UniverseIndex};
use rustc_middle::ty::{
CoercePredicate, RegionOutlivesPredicate, SubtypePredicate, TypeOutlivesPredicate,
};
@ -299,12 +300,13 @@ fn try_normalize_ty(
param_env: ty::ParamEnv<'tcx>,
ty: Ty<'tcx>,
) -> Option<Ty<'tcx>> {
self.try_normalize_ty_recur(param_env, 0, ty)
self.try_normalize_ty_recur(param_env, DefineOpaqueTypes::Yes, 0, ty)
}
fn try_normalize_ty_recur(
&mut self,
param_env: ty::ParamEnv<'tcx>,
define_opaque_types: DefineOpaqueTypes,
depth: usize,
ty: Ty<'tcx>,
) -> Option<Ty<'tcx>> {
@ -312,10 +314,26 @@ fn try_normalize_ty_recur(
return None;
}
let ty::Alias(_, projection_ty) = *ty.kind() else {
let ty::Alias(kind, projection_ty) = *ty.kind() else {
return Some(ty);
};
// We do no always define opaque types eagerly to allow non-defining uses in the defining scope.
if let (DefineOpaqueTypes::No, ty::AliasKind::Opaque) = (define_opaque_types, kind) {
if let Some(def_id) = projection_ty.def_id.as_local() {
if self
.unify_existing_opaque_tys(
param_env,
OpaqueTypeKey { def_id, args: projection_ty.args },
self.next_ty_infer(),
)
.is_empty()
{
return Some(ty);
}
}
}
// FIXME(@lcnr): If the normalization of the alias adds an inference constraint which
// causes a previously added goal to fail, then we treat the alias as rigid.
//
@ -331,7 +349,7 @@ fn try_normalize_ty_recur(
this.add_goal(normalizes_to_goal);
this.try_evaluate_added_goals()?;
let ty = this.resolve_vars_if_possible(normalized_ty);
Ok(this.try_normalize_ty_recur(param_env, depth + 1, ty))
Ok(this.try_normalize_ty_recur(param_env, define_opaque_types, depth + 1, ty))
}) {
Ok(ty) => ty,
Err(NoSolution) => Some(ty),